Debenzylation using catalytic hydrogenolysis in trifluoroethanol, and the total synthesis of (−)-raumacline

N-Debenzylations using catalytic hydrogenolysis often fail to take place unless alcoholic solvents are used, but this can lead to N-alkylation as a side reaction; using trifluoroethanol as the solvent overcomes this problem, and leads to highly reliable hydrogenolyses for a wide range of substrates, including the final deprotection step in our total synthesis of (−)-raumacline.     

Fourier transform infrared characterization of the azido complex of methane monooxygenase hydroxylase from Methylococcus capsulatus (Bath)

The azido complex formed in oxidized methane monooxygenase from Methylococcus capsulatus (Bath) was investigated with resonance Raman and FTIR techniques. These experiments show the presence of a nuas(NNN) at approximately 2077 cm-1 which splits to two components at 2059 and 2073 cm-1 with 15N14N2. The vibrational data are assigned to an azido complex bound terminally to one iron(III) at the diiron center. When the azido complex is illuminated at 15 K, a new nuas(NNN) is observed at 2136 cm-1 which is assigned to a photodissociated HN3 within the substrate pocket. We propose a model where an aqua ligand engages a hydrogen bond interaction with the 1N atom of the azido group and acts as at a proton donor during the photolysis process.     

Phase diagrams of lyotropic cholesteric fluids

Experimental investigations of lyotropic cholesterics fluids are presented which show that changes in the shape anisotropy and chirality of the micellar population determine the topology of the temperature-concentration phase diagrams. For given amounts of the substances which induce the chirality and modify the shape anisotropy of the micelles, two distinct biaxial cholesteric phases are disclosed in the phase diagrams. This is interpreted in the framework of the catastrophe theory of phase transitions.     

Continuous wave observation of massive polariton redistribution by stimulated scattering in semiconductor microcavities

A massive redistribution of the polariton occupancy to two specific wave vectors, zero and approximately 3.9x10(4) cm(-1), is observed under conditions of continuous wave excitation of a semiconductor microcavity. The "condensation" of the polaritons to the two specific states arises from stimulated scattering at final state occupancies of order unity. The stimulation phenomena, arising due to the bosonic character of the polariton quasiparticles, occur for conditions of resonant excitation of the lower polariton branch. High energy nonresonant excitation, as in most previous work, instead leads to conventional lasing in the vertical cavity structure.     

Inhibited emission in photonic woodpile lattices

The emission and transmission properties of realistic photonic-band-structure woodpile lattices are investigated by use of a scattering-matrix treatment. Lattices with three to nine layers are studied, and the results are interpreted with band-structure calculations for an infinite lattice. Calculations of the total radiative loss rate for a source within the lattice show that these structures can provide significant inhibition of emission, with values as low as 3% of the free-space value in the nine-layer structure.     

The NMR spectra and conformations of cyclic compounds–III: The conformations of some pinane derivatives

The 220 MHz ¹H spectra of isoverbanone, nopinone and verbanone are reported. The spectra of the first two are completely assigned but that of verbanone only partially. The coupling constants obtained provide information about the conformation of these molecules. The isoverbanone molecule is almost Y shaped, but that of nopinone is between a Y shape and a half-chair conformation with the six membered ring bent away form the gem dimethyl groups. These conformations are consistent with the known steric interactions in these molecules.     

Enhancement of Na+ diffusion in a bicontinuous cubic phase by the ionophore monensin

Pulsed field gradient spin-echo NMR diffusion and relaxation measurements were used to investigate how the Na+ ionophore monensin affected the dynamics of sodium ions in a Myverol 18-99/saline bicontinuous Ia3d cubic phase (BCP). The monensin Na+ binding number was estimated from 23Na line widths to be between 3 and 6. The dependence of the apparent Na+ diffusion coefficient on the concentration of monensin revealed monensin-induced Na+ transport. At high monensin concentrations, the enhancement of D(Na+) was offset by Na+-monensin binding. The greatest enhancement was measured at short diffusion times (delta < or = 5 ms), which we explain in terms of the bicontinuous topology of the cubic phase and a combination of tortuosity and bilayer permeability effects. We also propose numerical simulations which would enable the separation of the two effects. To our knowledge, this is the first study of ionophore-mediated cation diffusion in a bicontinuous cubic phase. The approach could be used to study the dynamics of hydrophilic species in the aqueous channels of BCPs and similar structures, as well as to measure the ion-transporting efficiency of ionophores.     

Synthesis and studies of a tetradecanuclear manganese(II)/(III) cage

A novel Mn14 cluster is reported; this is a new nuclearity for manganese cages and highly unusual in that the ligands are not exclusively oxygen donors.     

Photo‐initiated thiol–ene “click” hydrogels from RAFT‐synthesized poly(N‐isopropylacrylamide)

Despite the efficiency and robustness of the widely used copper‐catalyzed 1,3‐dipolar cycloaddition reaction, the use of copper as a catalyst is often not attractive, particularly for materials intended for biological systems. The use of photo‐initiated thiol‐ene as an alternative “click” reaction to synthesize “model networks” is investigated here. Poly(N‐isopropylacrylamide) precursors were synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization and were designed to have trithiocarbonate moieties as end groups. This structure design provides opportunity for subsequent end‐group modifications in preparation for thiol‐ene “click.” Two reaction routes have been proposed and studied to yield thiol and ene moieties. The advantages and disadvantages of each reaction path were investigated to propose a simple but efficient route to prepare copper‐free “click” hydrogels. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4626–4636